Unanswered questions about Tony Rezko, a friend and contributor, who is now on trial for corruption and extortion. Contradicted denials about a campaign adviser's contact with the Canadian government concerning NAFTA. And don't forget that lack of experience on national security.

The Hillary Clinton campaign seems rather satisfied with its current lines of attack against Barack Obama. On this morning's conference call with reporters, as voters in Ohio, Texas, Rhode Island, and Vermont were hitting the polls, top Clinton aides hammered these points repeatedly, noting they were pleased that reporters covering Obama were beginning to ask him about these matters. Obama has "credibility questions," asserted Phil Singer, who handles opposition research for the Clinton campaign. Howard Wolfson, the communications director, made much of the fact that the Obama campaign had sent an aide to take notes at the trial of Rezko, a developer indicted on corruption charges. His trial began yesterday. The aide's presence "belies the fact," Wolfson maintained, that Obama has downplayed his relationship with Rezko, who helped raised about $150,000 for Obama and who bought a strip of property next to Obama's home.

The Clintonites suggested that Obama could be a witness in the trial--though the list of expected witnesses made public on Monday did not include the Illinois senator--and Wolfson noted that Obama will continue to be "dogged by questions" related to Rezko unless he "answers them fully." Due to these "unanswered questions," Wolfson said, Democratic voters will not want to seal the deal with Obama.

The Obama campaign insists it has come clean on Rezko. Obama has said he was dumb to have participated in a real estate transaction with Rezko when it was publicly known he was under investigation. The campaign gave to charity the $150,000 in Rezko-related donations Obama. Its position: there are no unanswered questions about Obama and Rezko. Bill Burton, an Obama campaign spokesperson, says, "After months of reporting and the many questions asked and answered, it is well established that this is not a case about Senator Obama. Senator Obama knew Tony Rezko for two decades in very different circumstances, none of which involve the actions with which Mr. Rezko has been charged."

Still, the Clinton campaign claims there are "major questions." Such as, did Obama do favor for Rezko's business partners? Did Rezko help Obama allies get jobs? It could be that the answer to such questions is a simple "no." There's no evidence that has yet emerge to back up allegations of this sort. But that does not stop the Clinton campaign from posing questions and then claiming they are unresolved.

The bigger question is, will this matter to Democratic voters? As the Clinton aides discuss the Rezko case, the NAFTA dustup, and their recent assault on Obama's national security experience, it seems that they finally believe they have managed to grab hold of Obama's tail. But there's no way of knowing if voters are paying attention to these attacks and if such matters will be a drag on Obama. (He has taken a a dip in the Texas polls.) If Obama does not fare well in Ohio, Texas, Rhode Island and Vermont, the Clintonites will argue that the "unanswered questions" have slowed him down, and they will keep on firing them at Obama, as the campaign heads toward Pennsylvania on April 22 (188 delegates!). But if Obama wins one of the big states or more, he--that is, the voters--will answer the question about the "unanswered questions." Then what will the Clinton campaign ask next?